The present invention relates to a protective device for the occupants of a motor vehicle, especially of a passenger car, and, more particularly, to a protective device having a pressure vessel which serves for the storage of a pressurized gas and which is connected, via an outflow orifice provided in the pressure-vessel wall, to the interior of a bag inflatable by the gas. The outflow orifice is closeable via at least one valve consisting of a pressure-vessel wall piece surrounded by a predetermined breaking point and of a piston rod which is connected operatively to this wall piece. The piston rod projects on one side from a closed tripping cylinder filled with a pyrotechnic medium and is axially displaceable out of a first end position into a second by a piston arranged in the tripping cylinder when the pyrotechnic medium is ignited.
A protective device for an airbag system is shown in German Offenlegungsschrift No. 2,118,745. This device comprises a can-shaped, essentially cylindrical vessel having in its interior, and coaxially relative to its longitudinal mid-axis, a cylinder which is filled with pyrotechnic material and in which a piston connected firmly to a piston rod projecting from the cylinder on one side is so arranged that in the first end position of the piston rod, that is to say when the airbag system is not tripped, it can still cover a specific distance until its end face butts against the cylinder. The end of the piston rod facing away from the piston bears perpendicularly against a plate-like wall part of the cylindrical vessel which is surrounded by a predetermined breaking point. Consequently, when ignition occurs in the tripping cylinder, the piston rod is pressed violently by the piston, coming under pressure, against the wall part which breaks out at its predetermined breaking points and which causes the gas located in the pressure vessel to flow into the inflatable bag. To prevent the compressed gas from entering the bag too violently, the cylindrical vessel is surrounded by a second vessel equipped with a cover which is guided displaceably in the direction of the axis of the piston rod and covers the vessel and which is provided over its entire circumference with outlet holes for the escaping compressed gas. The compressed gas flowing out of the pressure vessel as a result of the violent breaking-open of the wall part is advantageously throttled and distributed. In an emergency, however, the cover acting as a distributor and guided telescopically on the inner vessel and on the outer vessel can jam.
Other types of protective devices as shown, for example, in German Offenlegungsschrift No. 2,305,908, possess similar plate-like valves which are blasted off on the end face of the pressure vessel when a propellent charge is ignited. Pressure vessels are also known, e.g. German Offenlegungsschrift No. 1,781,383, which can be arranged transversely relative t the direction of travel of the vehicle in an elongate recess in the vehicle dashboard. These pressure vessels are surrounded concentrically by an outer vessel provided with a horizontal slit-like outlet orifice and are broken open over their entire length along a horizontal predetermined breaking line as a result of the explosion of an explosive charge. In all these instances, an undesirable uncontrolled inflation of the impact bag facing the driver or the front passenger occurs.
An object on which the present invention is based is, therefore, to provide a protective device such that the undesirable violent escape of the compressed gas into the airbag is prevented.
This object has been achieved, in a protective device with a wall piece which is part of the wall of a hollow valve block provided with the outflow orifice. The wall piece is equipped with an extension projecting into the interior of the valve block, the piston rod is displaceable in the valve block transversely relative to the extension, and the extension is located in the path of movement of the piston rod.
As a result of this configuration, the wall piece is not torn out perpendicularly to the plane in which its predetermined breaking points lie, but pivoted relative to this plane. The wall piece pivots in a flap-like manner about initially remaining connecting points, before it can be torn out completely by the force of the outflowing compressed gas. Consequently, during axial displacement of the piston rod, sickle-like orifices first occur on two opposite sides of the loosening wall piece, and these increase in size until the entire valve orifice is opened. It thereby becomes possible to control the quantity of outflowing compressed gas and to keep it relatively small in the initial phase, before the entire available quantity of compressed gas flows out violently. The present invention consequently allows a perfect, fault-free deployment of the initially folded-together impact bag without fearing an obstruction caused by a jamming of mechanically guided parts, and also makes it possible to obtain a lefthand-twist characteristic line for the outflow.
Another advantage of protective devices constructed according to the present invention resides the outflow orifice covered by a cap-like cover, which itself is provided with outflow orifices, if the piston rod is equipped, at its end facing away from the actuating piston, with the cap-like cover projecting radially from it. In such an embodiment, the cover is lifted off directly from the piston rod and therefore in a fault-free manner from the outflow orifice, and can also deploy the impact bag mechanically to some extent in parallel with the quantity of compressed gas flowing out as a result of the actuation of the piston rod and serve as a kind of guide blade for the escaping compressed gas which can thereby be deflected in a controlled manner and enter the impact bag in a diffuser-like way.
The cover of the present invention can be equipped with an edge which extends parallel to the axis of the piston rod and which is held sealingly in the manner of a piston in a cylindrical recess of the valve block, as long as the piston rod is in the first end position. This embodiment allows a compact and stable closed configuration of the entire protective device which, in the non-actuated state, is protected against external influences, especially against possible soiling. The outflow orifices of the cover can be provided solely in its edge so that the desired deflection of the escaping quantity of compressed gas is achieved and the undesirable onrush of the central region of the impact bag in the direction of the person to be protected is prevented. These outflow orifices can also be configured as slits which extend from the free end of the edge towards the closed cover part and which have a circular rounding on their closed side.
As a result, the effect of a throttling of the quantity of compressed gas flowing out in the first few milliseconds can be further assisted, because the quantity of compressed gas cannot yet escape through the full cross-section of the outflow slits. To achieve as uniform a distribution as possible of the escaping compressed gas from these outflow slits, a perforated plate having a central recess for the piston rod can be fastened to the free continuous face of the edge.
The length of the edge measured parallel to the piston rod, can be so configured that it corresponds to the displacement travel of the piston rod out of the first end position into the second. With the piston rod extended, the cover with its edge has also come out of the guide completely, so that, in addition to the outflow slits, an annular region can also be provided for the outflowing compressed gas, if this is necessary.
An especially advantageous embodiment is provided if there are in the valve block two diametrically opposed wall parts with extensions which are aligned with one another and the free end faces of which are at a distance from one another somewhat greater than the diameter of the piston rod. It thus becomes possible to provide the maximum possible lever arm for the pivoting of the wall pieces without the space requirement becoming too great.
A sleeve-shaped pressure vessel, closed off by the wall of the valve block, can be connected respectively adjacent to each wall part in accordance with another advantageous feature of the present invention. This then results altogether in an elongate, approximately cylindrical vessel which has centrally, in its middle, the outlet orifice with the diffuser cover attached to the piston rod. Such embodiments are especially suitable for actuating the impact bag for the front passenger because, on account of its dimensions, it can even be accommodated unproblematically in the dashboard above the glove compartment generally to be arranged there.
The valve block can, however, also be surrounded by a tire-shaped pressure vessel which is arranged concentrically relative to the valve block and which is closed on its open inside by a cylindrical wall of the valve block according to another embodiment of the present invention. This affords a compact design but one which, in view of its dimensions, is more suitable for accommodation in the middle part of the steering wheel, i.e. for use as an impact bag for the driver.
In the above embodiments, at least the pressure vessels attached to the valve block can consist of a thin-walled material which is reinforced externally by a composite fiber winding enveloping the pressure vessels. The valve block itself can be produced from a forged hollow section with a greater wall thickness than the material of the pressure vessels. Aluminum or aluminum alloys in particular have proved especially advantageous for this, because the total weight of the protective device can thereby be kept low. This valve block can accommodate not only the outflow orifices but also other functional elements. It can be welded in a gas-tight manner to the pressure-vessel parts.
Both the filling orifice closable in a pressure-tight and gas-tight manner and a safety valve can be provided in the solid valve block. The pressure vessel or pressure vessels can be assigned a pressure sensor, for the continuous detection of the pressure prevailing in the pressure vessels which sensor is mounted either on the wall of the pressure vessels or directly on a wall of the valve block.